Bond pads are electrical terminals which connect an integrated circuit die or chip to the electrical system outside of the chip. The electrical connection is normally made by bonding electrical leads to the bond pad. The chip can then be connected to a larger circuit, such as a printed circuit board (PCB), with the leads making contact with the outside system.
The bond pads are integrally connected to metal lines or runners within the die, which are typically formed of a metal such as aluminum, aluminum-silicon eutectic, aluminum-copper alloys, or polysilicon. The bond pads themselves are also typically formed of aluminum or an aluminum alloy, which is highly conductive and relatively inexpensive. Unfortunately, aluminum or aluminum alloy readily oxidizes to form aluminum oxide. The aluminum oxide is not conductive, and it therefore increases the overall resistivity of the system. Increased resistivity, in turn, leads to slower signal propagation.
Conventionally, aluminum oxide is removed with a reducing agent in several separate steps. The chip is exposed to atmosphere between steps, and the exposed metal spontaneously oxidizes, impairing the conductive connection. Even the short exposure between oxide cleaning and sealing the bond pad results in aluminum oxide formation between the metal and sealant.
There is thus a need for a method of avoiding oxide on the surface of a contact pad.